1. Field of the Invention
The invention relates to a method for displaying a moving image on a display, wherein all pixel lines of the display are addressed in each case during image periods for displaying image information, and a backlight for displaying the image information backlights the pixel lines.
2. Description of the Related Art
A backlight which generates light by means of cold cathode fluorescent lamps (CCFL) situated in rows is typically used for backlighting an LCD screen. The light radiates in all directions in the display, and a reflector is provided which reflects the back-radiated light in the direction of the LCD screen. Such a display may be used, in particular, in the medical field, in which a high contrast in image displays is desirable for the purpose of diagnosis. In addition, for this application, a low level of motion blurring of a moving image on an LCD screen of the display is desirable.
LCD screens belong to the so-called hold-type displays, whose image content is retained for the duration of one frame (one image period). Because of the reaction time of approximately 8 ms, for example, of the liquid crystals of the LCD screen, which represents the time for changing the brightness of an image pixel from 10% to 90%, an addressed image line does not immediately illuminate with the “correct” brightness. As a result, the edges of a displayed moving object appear blurred or indistinct to an observer for the duration of the display due to brightness integration. This interfering of blurring of movement is also intensified due to the fact that the actual motion of an object which may be represented on the display is beyond the limit of resolution by the human eye. The human eye typically detects a distance of approximately 0.15 mm, whereas an addressed scan line at an image refresh rate of 60 Hz is visible to the human eye for a duration of approximately 17 ms, during which time the moving object which is moving at a speed of 0.1 mm/s, for example, traverses a distance of 1.7 mm.
A blinking backlight is described in the publication titled “Rasante Zeiten, Techniken zur besseren Bewegtbilddarstellung auf Flachbildschirmen” [“Fast Times: Techniques for Improved Moving Image Displays on Flat Screens”], c't 2005, Issue 9. The blinking backlight temporarily switches off the background lighting before the end of a frame, thus reducing the light intensity to zero after illumination of an image and thereby decreasing the brightness integral and thus also decreasing blurring of the edges. A disadvantage is that so-called leading and trailing ghost images of the moving object are visible if the liquid crystals (pixels) are not yet aligned and still contain information from a previous image, or if the liquid crystals have realigned and therefore already contain information for a next image. A moving image display may be enhanced by use of a scanning backlight, in which lighting means, such as lamps, provided in rows are switched on and off during an image period on a line-by-line basis in synchronization with the image loading. A disadvantage is that a plurality of lighting means provided in rows is necessary.
German patent application 10 2007 009 014.7 proposes a method for displaying a moving image on an LCD screen, wherein all pixel lines are addressed during each image loading. The display of moving images is enhanced by the fact that after a waiting period, a backlight provides backlighting following each image loading. It is disadvantageous that the “electrical” as well as the “optical” frames are extended, which requires complex electronics.